1. Field of the Invention
The present invention relates generally to vibratory finishing machines, and more particularly to a novel and improved bowl-type vibratory finishing machine.
2. Prior Art
Many surface finishing operations such as deburring, burnishing, descaling, cleaning and the like can be conducted expeditiously in a vibratory finishing machine. Such a machine includes a movably mounted receptacle and a drive system for vibrating the receptacle. Workpieces to be finished are loaded into the receptacle together with finishing media. A finishing action is imparted to the workpieces by vibrating the receptacle so that the mixture of workpieces and media is effectively maintained in a fluid or mobile state with smaller components of the mixture dispersed between large components for impact. Impulse forces imparted to the mixture not only cause repeated impacts among its components but also cause the mixture to churn in a predictable manner as a finishing process is carried out.
Two basic types of vibratory finishing machines are in common use. One type employs an elongated, substantially horizontally disposed receptacle which is vibrated by eccentrics rotating about horizontal axes paralleling the length of the receptacle. This first type of machine is known in the art as a "tub-type machine" or simply "tub machine", and its receptacle is commonly called a "tub". Another type uses a substantially annular receptacle which is vibrated by rotating one or more eccentrics about a vertical "center axis" located centrally of the receptacle when the receptacle is at rest. This latter type of machine is known in the art as a "bowl-type machine" or simply "bowl machine", and its receptacle is commonly called a "bowl". While tub and bowl machines have many similar characteristics, they are sufficiently different in arrangement and operation that one will frequently offer advantages over the other in solving a particular finishing problem. The present invention relates to bowl-type machines.
During operation of a bowl machine, the bowl vibrates in gyratory movements about a node or null point located somewhere along the machine's center axis. This gyratory movement subjects the bowl's contents to a complex of vertical, radial and tangential impulse components which are intended to effect a uniform dispersion of the smaller components of the workpiece and media mixture among the large components of the mixture for impact. The resultant impulses are so oriented and timed as to cause both circumferential precession of the mixture and rotation of the mixture in essentially radiating vertical planes.
Those skilled in the art maintain different and conflicting theories on where the node or null point should be located along the center axis. Some maintain that the node or null point should be located within or near a horizontal plane which includes the center of gravity of the bowl's contents. This arrangement effectively minimizes horizontal impulse components imparted to the bowl's contents and maximizes the vertical components. Others maintain that a node or null point location slightly below the bottom of the bowl's chamber is desirable since it gives something of a mix of vertical, horizontal and tangential components. Still others advocate higher and lower node or null point locations.
Those skilled in the art similarly advance different and conflicting theories on the number of eccentrics which should be used to vibrate the bowl, the locations of the eccentrics, and the relative orientations of the eccentrics where more than one is used. Still other theories obtain on how and where a drive motor should connect with the eccentrics.
Factors such as node or null point location, the number, location and arrangement of eccentrics, and features of the drive motor connection all intertwine to determine such other factors as:
(a) the simplicity or complexity of the machine;
(b) the ease with which the machine can be serviced and such parts as bearings replaced;
(c) the longevity of service which can be expected from the machine;
(d) the sensitivity of the machine to different bowl loadings, i.e. whether it can handle a wide range of large and small, heavy and light loads; and
(e) the type of vibratory movement which is imparted to the bowl, which, in turn, determines such things as:
(i) the type of circulation movement which will be executed by a mixture of media and workpieces in the bowl;
(ii) the direction and rate of precession of the mixture; and
(iii) the effectiveness of the resulting finishing action in terms of quality and time required to carry it out.
Previous proposals made in an effort to optimize these factors have resulted in machines which are relatively complex and difficult to service. The need for frequent bearing replacement has been a continuing problem, and the construction of many such machines has made bearing replacement difficult. Most bowl machines are quite sensitive to changes in bowl loading and operate effectively only in a relatively narrow loading range.
Most vibratory finishing machines are provided with a lining which prevents metal workpieces from impacting on the metal shell of the receptacle. Inasmuch as the lining material is abraded away during extensive machine use, replaceable liners have been proposed. A problem encountered in the use of replaceable liners is that of clamping and holding them securely in position so that they do not shift or separate from the receptacle shell under the influence of extensive vibration. A solution which has successfully solved this problem in tub-type machines is described in the referenced Replaceable Liner Patent.
Bowl-type machines present peculiar lining problems not found in tub-type machines. Whereas tub machines have elongated tubs of relatively simple configuration, bowl machines have relatively complex, torroidal-shaped bowls. Molding a replaceable, torrus shaped liner is difficult and expensive. Moreover, an acceptable solution is not found in prior proposals to the problem of adequately clamping a torrus shaped liner in place so that it will withstand extensive vibrations without employing a structure which significantly complicates liner replacement.
Most bowl machine proposals use a cast-in-situ liner which requires extensive machine disassembly and replacement of the bowl's shell when a liner is to be changed. The expanse and effort and lengthy down-time required to replace bowl machine liners is, in fact, one of the major drawbacks whih influence purchasers to buy a tub-type machine when a bowl-type machine might better serve their needs.
The use of a strainer plug which cooperates with a receptacle liner to close portions of a drain opening formed in the bottom of the liner is described in the referenced Plug Patent. The described drain closure system includes a strainer plug carried by the liner itself, and a closure plug which is clamped against the underside of the machine's metallic receptacle. Both of the plugs must be removed if one is to fully open the drain opening. While the described system operates quite efficiently as a drain for fluids and as a strainer to remove fines, it is not well adapted to serve as a means of discharging finishing media from the receptacle due to the difficulty one would have in removing the strainer plug from the liner in the presence of such media.